This application claims the benefit of the Korean Application Nos. 2001-87877 filed on Dec. 29, 2001 and 2002-82989 filed on Dec. 24, 2002, which are hereby incorporated by references.
1. Field of the Invention
The present invention relates to a metallic nanoparticle cluster ink and a method for forming a conductive metal pattern using the cluster ink. More specifically, the present invention relates to a metallic nanoparticle cluster ink comprising colloidal metallic nanoparticles and a bifunctional compound, and a method for forming a conductive metal pattern comprising the steps of forming a metallic nanoparticle pattern on a substrate using a mold made from PDMS (poly(dimethylsiloxane) polymer as a stamp, and heat-treating the substrate.
2. Description of the Related Art
A variety of methods for forming conductive metal patterns are currently used in various industrial fields. For example, the conductive metal patterns are formed by photolithography methods using a photoresist, silk screen methods using a metal paste, etc. However, according to the recent industrial and technological development, there is a need for methods capable of forming conductive metal patterns in a simple, convenient and cost-effective manner. From these views, special attention has been paid to a micro-contact painting technique.
The micro-contact printing technique is a process for forming a pattern by stamping the pattern on a substrate. Herein, a mold made from PDMS polymer is used as a stamp and an organic molecule or an organic metal compound/colloidal metallic nanoparticles is used as ink. According to the micro-contact printing technique, the pattern in size of 0.1-100 microns can be easily formed (see, Angew. Chem. Int. Ed., 1998, vol. 37, p. 550).
The PDMS stamp is advantageous in that it has low surface energy, high chemical stability, and excellent formability into various shapes. Accordingly, various methods using the PDMS stamp have been developed.
For example, U.S. Pat. No. 6,048,623 is disclosing a method for forming a metal pattern comprising forming self assembly monolayer by transferring organic molecular with a functional group capable of binding with a metal surface, onto the substrate and etching unpatterned area chemically. At this time, the organic self assembly monolayer acts as a resist during chemical etching.
U.S. Pat. Nos. 3,873,359, 3,873,360 and 3,900,614 disclose a method for forming a metal pattern on a substrate comprising forming a pattern of organic metal compound/colloid metallic nanoparticles having catalytic activity in a micro-contact printing method, and treating the pattern through an electroless plating process to form a resultant metal pattern by catalysis of the organic metal compound. In this method, micropatterns is formed in a simple and cost-effective manner, without the use of complicated lithography systems.
Unlike above-mentioned methods, Chemistry of Materials (2001, vol. 13, p. 87) discloses a different method for forming a metal thin film using metallic nanoparticles, wherein a plurality of gold nanoparticle self assembly monolayers are stacked on a substrate, followed by heat-treating the monolayers at a temperature of 250-350° C. In addition, similar methods are disclosed in Korean Patent Laid-Open Publication No. 1998-025037, etc.
However, conventional micro-contact printing techniques using a metallic nanoparticle colloid as ink is disadvantageous in that the use of only the metallic nanoparticle colloid makes it difficult to form a high quality thick pattern because metallic nanoparticles are widely dispersed in the colloid. In addition, it is difficult to obtain high conductivity in the case of conductive metal pattern.